The present invention relates to a narrow band ultraviolet laser device.
In an ultraviolet laser device, an art of band-narrowing, which narrows a spectral bandwidth of laser light and stabilize its center wavelength by mounting a wavelength selection element in a resonator, is conventionally known (Refer to, for example, Japanese Patent Laid-open No. 10-313143).
Hereinafter, the prior art will be explained with an excimer laser device as an example. FIG. 7 is an explanatory block diagram of a narrow band excimer laser device 1 according to the prior art. In FIG. 7, the excimer laser device 1 includes a laser chamber 2 with a laser gas being sealed therein, and a band-narrowing unit 10 for narrowing a bandwidth of laser light 11 oscillated from this laser chamber 2. The laser light 11 oscillated by electric discharge inside the laser chamber 2 is incident on the band-narrowing unit 10 provided outside and behind the laser chamber 2.
The laser light 11 incident on the band-narrowing unit 10 is expanded by prisms 32 and 32, and is incident on a grating 33. Only the laser light 11 with a predetermined wavelength is returned in the same direction as the incident light by the grating 33, then it is incident on the laser chamber 2 again and is emitted from a front mirror 8. Subsequently, it is incident on a processing machine 15 to be a light source for performing precision machining inside it.
In this situation, part of the laser light 11 sometimes hits on end portions of the prisms 32 and the grating 33 inside the band-narrowing unit 10. When such reflected light the bandwidth of which is not narrowed (this is called undesired laser light 11A) returns to the laser chamber 2, optical quality of the laser light 11 such as a center wavelength, spectral bandwidth, and the like is degraded. Further, as a result that the laser light 11 is incident on an optical component from the surfaces other than a predetermined incident surface, heat sometimes generates and thereby the optical component is deformed. Furthermore, when the laser light 11 is incident on the grating 33 at the angles other than a predetermined incident angle, wavelength selection by the grating 33 is not favorably performed, and thereby the optical quality of the laser light 11 is degraded.
In order to avoid the above, a first light shielding element 37A for removing the undesired laser light 11A is provided at a position where the laser light 11 is incident on the band-narrowing unit 10, and a second light shielding element 37B is provided inside the band-narrowing unit 10. Further, a third light shielding element 37C is provided inside the front mirror 8 to shape a beam form of the laser light 11 into a predetermined form suitable for processing.
FIG. 8 shows the forms of the light shielding elements 37A to 37C. In FIG. 8, the light shielding elements 37A to 37C have light shielding sections 49A to 49C in a plate form for removing the undesired laser light 11A, and light transmitting sections 47A to 47C constituted by rectangular openings for transmitting the laser light 11, respectively. When the laser light 11 is radiated to the light shielding elements 37A to 37C, the undesired laser light 11A hit on the light shielding sections 49A to 49C is irregularly reflected, then deviated from an optical path, and is absorbed in a cover or the like not shown for covering the excimer laser device 1. The residual laser light 11 passes through the light transmitting sections 47A to 47C, and is shaped into a rectangular beam form.
However, the above-described prior art has the disadvantages as described below.
Specifically, according to the prior art, there is no description regarding the material of the light shielding elements 37A to 37C, and metal is generally used. When the laser light 11 is radiated to the light shielding elements 37A to 37C, part of it is absorbed in the light shielding sections 49A to 49C, and the light shielding sections 49A to 49C are beginning to have heat. In this situation, gases, such as, for example, air and an inert gas exist inside the light transmitting sections 47A to 47C. Accordingly, temperature gradient occurs to the gases as a result of heat generation from inner edges 50A to 50C of the light shielding sections 49A to 49C. Specifically, the temperature of the gases near the inner edges 50A to SOC of the light transmitting sections 47A to 47C rises to be high, but the temperature of the gases near a center does not rise so much.
As a result, indexes of refraction of the light transmitting sections 47A to 47C become nonuniform, and the gases act as if they were lenses, whereby a wavefront of the laser light 11 passing through the light transmitting sections 47A to 47C is distorted. Thus, there arises the disadvantage that the beam form of the laser light 11 emitted from the excimer laser device 1 is distorted or the spectral bandwidth is increased, thereby degrading the quality of the laser light 11, and processing is not favorably performed.
Further, temperature gradient hardly exists at the time of the start of the laser oscillation, but as the laser light is oscillated for a long period of time, the temperature gradient occurs to balance, and therefore the indexes of refraction of the light transmitting sections 47A to 47C at the time of the start of the oscillation changes after a lapse of long period of time. Thus, even if the incident angle of the laser light 11 onto the grating 33 is adjusted so that the optical quality becomes favorable at the time of start of oscillation, the wavefront is distorted with a lapse of time, and the optical quality is degraded. Further, there exists the disadvantage that the beam form and the beam center position are varied to give an adverse effect on processing.
The present invention is made in view of the above-described disadvantages, and its object is to provide a narrow band ultraviolet laser device which can restrict a change in temperature gradient at light transmitting sections and maintain laser light at a high grade.
In order to attain the above-described object, a first aspect of an ultraviolet laser device according to the present invention is a narrow band ultraviolet laser device comprising light shielding elements having
light transmitting sections each constituted by an opening for transmitting laser light, and
light shielding sections that surround the light transmitting sections, remove undesired laser light from an optical path and shape the laser light into a predetermined form, and
includes the constitution in which healing means for heating the light transmitting sections are included in the vicinity of the light shielding elements.
According to the above constitution, the heating means for heating the light transmitting sections are included in the vicinity of the light shielding elements. Consequently, gases inside the light transmitting sections are entirely heated and become substantially uniform in temperature, thus making it possible to reduce temperature gradient of the gases inside the light transmitting sections, which occurs when the laser light is radiated to the light shielding plate. Accordingly, ununiformity in the indexes of refraction of the light transmitting sections is reduced, and therefore a wavefront is not distorted when the laser light passes through the light transmitting sections, thus making it possible to obtain the laser light at a high grade. Further, by heating the entire heat shielding elements in advance, a change in the indexes of refraction of the light transmitting sections between the time of starting laser light oscillation and the time after a lapse of time can be reduced. Accordingly, if the positions and the angles of the optical components in the band narrowing unit at the time of start of oscillation are adjusted, a change in the wavefront with a lapse of time is small, and the optical quality is not degraded.
Further, in the ultraviolet laser device, the heating means may also perform heating in a stale in which the laser light is not oscillated.
According to the above constitution, the temperature of the gases inside the light transmitting sections is already made substantially uniform when the laser light is oscillated, and therefore a change in the temperature of the gases immediately after the oscillation is reduced. Accordingly, the laser light at a high grade can be obtained with stability from the time immediately after the oscillation.
Further, the ultraviolet laser device may have the constitution including a laser controller for controlling laser oscillation, and
temperature measuring devices for measuring temperature of gases inside the light transmitting sections, in which the temperature measuring devices give information regarding the temperature of the gases to the laser controller, and the laser controller starts laser oscillation based on the information.
According to the above constitution, laser oscillation is started based on the information regarding the temperature of the gases, for example, the information that the temperature of the gases inside the light transmitting sections is sufficiently high. Consequently, the temperature of the gases inside the light transmitting sections already rise and is made approximately uniform when the laser oscillation is started, and therefore the laser light is not influenced by a variation of the index of refraction caused by a change in temperature, thus making it possible to always obtain the laser light at a high grade.
A second aspect of the ultraviolet laser device according to the present invention is a narrow band ultraviolet laser device comprising light shielding elements
having light transmitting sections for transmitting laser light, and
light shielding sections that surround the light transmitting sections, remove undesired laser light from an optical path and shape the laser light into a predetermined form, and has the constitution in which
spraying means for spraying an inert gas is included in the vicinity of the light shielding elements.
According to the above constitution, an inert gas is sprayed to the light shielding elements. Consequently, as the gases do not remain inside the light transmitting sections of the light shielding elements, the heated gases are always exchanged, and therefore the temperature gradient of the gases become gentle, thus reducing the refraction index gradient at the light transmitting sections. Accordingly, it hardly happens that the wavefront of the laser light is distorted, and the laser light can be maintained at a high grade. Further, for example, if the inert gas is cooled in advance, an increase in heat of the light shielding elements due to radiation of the laser light can be reduced to be small. Accordingly, the refraction index gradient at the light transmitting sections becomes small and distortion at the wavefront of the laser light becomes small.
A third aspect of the ultraviolet laser device according to the present invention is a narrow band ultraviolet laser device comprising light shielding elements
having light transmitting sections for transmitting laser light, and
light shielding sections that surround the light transmitting sections, remove undesired laser light from an optical path and shape the laser light into a predetermined form, and has the constitution in which
the light shielding sections are formed of a material including at least any one of aluminum, aluminum alloy and copper.
According to the above constitution, the light shielding sections of the light shielding elements are formed of a material including any one of aluminum, aluminum alloy and copper with good heat conductivity. Consequently, when the laser light is radiated to the light shielding elements, generated heat is conducted in a short time. In addition to this, aluminum and aluminum alloy reflect the laser light at a high reflectivity, and thus the laser light is hardly absorbed in the light shielding elements. For these reasons, an increase in heat at the inner edges of the light shielding sections is very small, and therefore ununiformity of the temperature hardly occurs to the gases inside the light transmitting sections, whereby the indexes of refraction become uniform. Accordingly, disturbance of the wavefront does not occur when the laser light passes through the light transmitting sections, thus making it possible to maintain the optical quality of the laser light at a high grade.
A fourth aspect of the ultraviolet laser device according to the present invention is a narrow band ultraviolet laser device comprising light shielding elements
having light transmitting sections for transmitting laser light, and
light shielding sections that surround the light transmitting sections, remove undesired laser light from an optical path and shape the laser light into a predetermined form, and has the constitution in which
the light shielding sections are formed of a material which transmits the laser light and have a function of removing the undesired laser light from the optical path.
Further, in the ultraviolet laser device, the removing function may be performed at total reflection coating formed on surfaces of the light shielding sections.
According to the above constitution, since the light shielding sections are formed of a material transmitting the laser light, such as, for example, CaF2, and synthetic fused silica, the laser light is not absorbed in the light shielding sections, and the light shielding sections hardly have heat. Accordingly, even if the gases are inside the light transmitting sections, the gases are not warmed and the indexes of refraction become uniform, whereby disturbance of the wavefront does not occur when the laser light passes through the light transmitting sections. Specifically, it is possible to maintain the optical quality of the laser light at a high grade. Further, by applying the total reflection coating to the surfaces of the light shielding sections, the laser light is reflected at high reflectivity, and thus the undesired laser light causing degradation of the quality of the laser light can be removed efficiently.
A fifth aspect of the ultraviolet laser device according to the present invention is a narrow band ultraviolet laser device comprising
light shielding elements for removing undesired laser light from an optical path and shaping laser light into a predetermined form, and
light transmitting sections formed by the light shielding elements, for transmitting the laser light, and has the constitution in which
the light shielding elements are formed of a material which transmits the laser light, and have a function of removing the undesired laser light from the optical path.
Further, in the ultraviolet laser device, the removing function may be a function of refracting the laser light at the light shielding elements and guiding it outside from the optical path as the undesired laser light.
According to the above constitution, the light shielding elements are constituted by a substance transmitting the undesired laser light, and therefore, if the undesired laser light is refracted at the light shielding sections, this can be absorbed in, for example, an absorber and the like, whereby the undesired laser light does not return to the optical path. In addition, since the undesired laser light passes through the light shielding elements, heat is not absorbed in the light shielding elements.
A sixth aspect of the ultraviolet laser device according to the present invention is a narrow band ultraviolet laser device comprising light shielding elements having
light transmitting sections for transmitting laser light, and light shielding sections that surround the light transmitting sections, remove undesired laser light from an optical path, and shape the laser light into a predetermined form, and has the constitution in which
the light transmitting sections are formed of a solid which transmits the laser light.
According to the above constitution, the light transmitting sections are constituted by a solid which transmits the laser light, such as, for example, CaF2, synthetic fused silica and the like. Consequently, since gases do not exist in the light transmitting sections through which the laser light passes, temperature gradient of the gases doesn""t occur. Further, since the light transmitting sections transmit the laser light at high transmissivity, it doesn""t happen that the laser light is absorbed in the light transmitting sections and warmed. Accordingly, it never happens that the temperature gradient occurs to the light transmitting sections and the indexes of refraction become nonuniform, and therefore disturbance of the wavefront does not occur when the laser light passes through the light transmitting sections. In this situation, for example, if metal plates that reflect the laser light at high reflectivity or optical components with the total reflection coating being applied thereto are placed around the light transmitting sections as the light shielding sections, the undesired laser light causing degradation of the quality of the laser light can be efficiently removed. Accordingly, the optical quality of the laser light can be maintained at a high grade.